The main aim of this thesis was to obtain information on the distribution and prevalence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in Atlantic Canada at both a regional Veterinary Teaching Hospital (VTH) and a regional diagnostic laboratory, as well as exploring culture methods for the detection of this pathogen. The strain type distribution of MRSP using the direct repeat unit (dru) typing approach in isolates collected at a regional diagnostic laboratory in Atlantic Show moreThe main aim of this thesis was to obtain information on the distribution and prevalence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) in Atlantic Canada at both a regional Veterinary Teaching Hospital (VTH) and a regional diagnostic laboratory, as well as exploring culture methods for the detection of this pathogen. The strain type distribution of MRSP using the direct repeat unit (dru) typing approach in isolates collected at a regional diagnostic laboratory in Atlantic Canada is described in Chapter 2. Ninety-four isolates were successfully typed and demonstrated to belong to 18 different dru types. The majority of isolates belonged to dt11a (30.9%), dt10h (24.5%), dt9a (18.1%), and dt11af (10.6%). The remaining 15.9% isolates were distributed between 13 different dru types, nine of which have not been previously identified: dt5k, dt6t, dt8ag, dt9ba, dt9bd, dt10bz, dt10cc, dt10cj, and dt11ca. The predominant dru types identified in this study were similar to those found in Ontario, Canada; however, cluster 9a appears to be less common in Atlantic Canada. A significant difference in the distribution of clusters between provinces was detected (p = 0.01). Notably, differences in the dru types were observed between Newfoundland and the Maritime provinces (New Brunswick, Nova Scotia, and Prince Edward Island). Cluster 10h was not present in the isolates from Newfoundland, while it was the predominant cluster in samples from PEI. Cluster 11a was the predominant cluster in both New Brunswick and Nova Scotia. Resistance to ≥2 antimicrobials (in addition to β- lactams) was observed in 71.4% of the isolates, with isolates belonging to cluster 9a being significantly more resistant to all antimicrobials tested except fusidic acid, chloramphenicol, and doxycycline. This study confirms that dru type distributions can vary significantly across the same country, and previously unreported dru types were identified in Atlantic Canada. Chapter 3 describes the presence of MRSP in a regional VTH environment after cleaning and disinfection and its potential to cause hospital-acquired infections. MRSP was isolated from 16/137 (12% [95% CI 6.8%–18.3%]) of environmental samples after the first cleaning and disinfection cycle, and 1/14 (7% [95% CI 0.2%–36.0%]) of environmental samples after the second cleaning and disinfection cycle. Culture results and data retrieved from medical records implicated a hospital-acquired MRSP infection involving two canine patients. Pulsed-field gel electrophoresis (PFGE) revealed that the MRSP isolates from these patients were clonal, further supporting a hospital-acquired infection. Since the same hospital personnel handled the MRSP positive patients in this case, transmission between patients was most likely via hospital personnel. PFGE of strains cultured from the environment and patient revealed that environmental strains were clonal to those from the patient associated with that area; however, non-clonal strains were also recovered from the same environmental area. The presence of MRSP in the hospital environment after cleaning and disinfection and a suspected hospitalacquired infection highlights the importance of a robust infection control program in these facilities. In Chapter 4, the prevalence of MRSP in clinical samples collected from dogs deemed high-risk for MRSP was estimated. This chapter also compared four culture methods for MRSP: traditional culture, mannitol salt agar with 2μg/mL oxacillin (MSAox), mannitol salt enrichment broth (EB) and MSAox, and EB and traditional culture. A total of 741 samples were analyzed from 556 individual dogs between February 2013 and April 2014. The prevalence of MRSP in samples detected by any method was estimated at 13.4% (95% CI 11.1%–16.0%). When prevalences were compared according to culture methods, EB and MSAox had the highest prevalence (11.2% [9.1%–13.7%]), followed by EB and traditional (10.8% [8.8%–13.2%]), then traditional (10.1% [8.1%–12.5%]), with MSAox having the lowest prevalence (8.9% [7.1%–11.2%]). MRSP prevalence using the traditional culture did not differ significantly from any of the three selective culture methods. Culture with MSAox detected significantly fewer MRSP than either of the enrichment broth methods. The addition of enrichment broth to current methodology is recommended, particularly in patients with a previous history of MRSP positive specimens. These results highlight how differences in culture methodology can influence prevalence estimates; therefore, caution should be exercised when comparing studies investigating prevalence. The MSAox had a low sensitivity for the detection of MRSP at 24 and 48 hours, and is not recommended as a rapid culture-based screening tool. The estimated MRSP prevalence in this study is similar to findings of previous studies in Canada and other parts of the world. Show less